This application is based on application No. Hei 9-143993 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a control circuit and a control method of a driving apparatus using a transducer.
2. Description of the Related Art
Conventionally, a variety of driving apparatuses using a piezoelectric element have been proposed.
FIG. 1 is an exploded perspective view of a prior art linear movement type driving apparatus, while FIG. 2 is an overall perspective view of the driving apparatus shown in FIG. 1. A driving apparatus 10a is provided with a fixed member 24, a piezoelectric element 22, a driving shaft 26 slidably supported in its axial direction by the fixed member 24 and a driving unit 28 to be connected to a stage (not shown) which moves with a driven member of, for example, a component placed on it. The piezoelectric element 22 is a sort of electromechanical transducer, the length of which is varied by voltage application. The piezoelectric element 22 has one end surface 22a affixed to the fixed member 24 in the direction in which it extends or contracts and has the other end surface 22b affixed to one axial end surface 26a of the driving shaft 26 in the direction in which it extends or contracts. The driving unit 28 is provided with a leaf spring 28a, and the driving unit 28 is frictionally coupled with the driving shaft 26 by the urging force of this leaf spring 28a. In this driving apparatus 10a, the driving unit 28 is moved in a specified direction along the driving shaft 26 when the driving shaft 26 is vibrated in a reciprocating manner in the axial direction by applying to the piezoelectric element 22 a periodic pulse voltage having a sawtooth waveform, for example.
For the purpose of applying a sawtooth-shaped pulse voltage to an electromechanical transducer, or to the piezoelectric element 22 of this driving apparatus 10a, a driving circuit 50 shown in FIG. 3 is used. This driving circuit 50 is constructed by combining a low-speed charging circuit, a high-speed discharging circuit, a low-speed discharging circuit and a high-speed charging circuit, and it has the advantage that its circuit can be compacted as compared with a driving circuit of a type which forms a sawtooth-shaped pulse by means of a digital circuit and further amplifies this pulse.
The driving circuit 50 has a first circuit 52 for driving in a first direction and a second circuit 54 for driving in a second direction opposite the first direction.
The first circuit 52 is constructed of switches C and D and a constant-current section 56. One terminal of the switch C is connected to a power source for supplying a constant voltage Vs, and the other terminal of the switch C is connected to one terminal of the constant-current section 56. The other terminal of the constant-current section 56 is connected to one terminal of the switch D and to one terminal of the piezoelectric element 22, and the other terminal of the switch D and the other terminal of the piezoelectric element 22 are connected to the ground.
The second circuit 54 is constructed of switches A and C and a constant-current section 56. One terminal of the switch A is connected to the power source for supplying the constant voltage Vs, and the other terminal of the switch A is connected to one terminal of the switch B and to one terminal of the piezoelectric element 22. The other terminal of the switch B is connected to one terminal of the constant-current section 56, and the other terminal of the constant-current section 56 is connected to the ground.
This driving circuit 50 applies a periodic sawtooth-shaped pulse voltage to the piezoelectric element 22 as shown in FIG. 4 when driving the driving apparatus in the first direction. This voltage waveform is generated by forming a low-speed charging circuit by closing the switch C, thereafter opening the switch C and then closing the switch D thus forming a high-speed discharging circuit.
In this case, as shown in FIG. 4, the driving speed can be varied by changing the duration of only low-speed charging duration t1, t2, t3 during which time the switch C is closed and making constant at all times a duration t4 starting from the start of the low-speed charging to the start of high-speed discharging at which point the switch D is closed. That is, if the low-speed charging duration is reduced in the order of t1xe2x86x92t2xe2x86x92t3 as indicated by waveforms {circle around (1)}, {circle around (2)} and {circle around (3)} of the piezoelectric element voltage in FIG. 4, then a voltage VH to be supplied to the piezoelectric element 22 is reduced, so that the driving speed becomes low, or slow.
However, according to this control method, as shown in the voltage-to-speed characteristic of FIG. 5, the inclination of the characteristic line becomes steep. Furthermore, a voltage VB of the piezoelectric element 22 when the driving apparatus starts driving becomes high. Therefore, the resolution of the driving speed cannot be made excessively high. Furthermore, the speed stability during low-speed driving is bad.
The object of the present invention is to provide a driving control apparatus and driving control method whose resolution of driving speed and speed stability at low speed are improved.
Specifically, the driving control apparatus of the present invention is a driving control apparatus for use in a driving apparatus comprising an electromechanical transducer which extends and contracts in a specified direction, either a fixed body or a moving body connected to one end in a direction in which the electromechanical transducer extends or contracts; a driving frictional member connected to the other end in the extension/contraction direction of the electromechanical transducer; and the other one of either the fixed body or the moving body frictionally coupled with the driving frictional member.
The driving control apparatus of the present invention comprises a driving pulse generating means including a high-speed electrifying circuit and a low-speed electrifying circuit connected to the electromechanical transducer; and a controller which sets a low-speed electrification time to a first specified time, sets a time from a low-speed electrification start time to a high-speed electrification start time to a second specified time, makes the low-speed charging duration shorter than the first specified time during low-speed driving and makes a time period from a low-speed charging start time to a high-speed discharging start time shorter than the second specified time, thereby controlling the electrification timing. An approximately sawtooth-shaped pulse voltage formed by low-speed electrification by means of the low-speed electrifying circuit of the driving pulse generating means and the high-speed electrification by means of the high-speed electrifying circuit of the driving pulse generating means is applied to the electromechanical transducer to extend or contract the same, thereby driving the moving body in a specified direction with respect to the fixed body.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.